Bit locking screw



A. L. LEE

BIT LOCKING SCREW Filed May 10, 1935 Illlllllllllllllllllllfillllllllllllllllllllllllllllll //II ////I //II I/II/I/ v Ignl 4/ Ma a hm INVENTOR Patented June 30, 1936 UNITED STATES PATENT OFFICE -2 Claims.

This invention relates to a set-screw, and setscrew assembly, for locking tools in operative position in a tool holding block, and has found particular usefulness in locking the cutter bit, or pick, of a coal-cutting chain in its receiving and supporting bit block.

In mounting tools of various types, and as general practice in mounting the bits, or picks, of a coal-cutting chain, a solid tool-carrying block is provided with a recess for receiving the tool, and with a threaded bore leading from the exterior of the block to the tooth-receiving recess. A set-screw having a threaded engagement in the bore of the bit block is caused to bear directly, or indirectly, against the bit, to lock it in position in the block.

As used for purposes in which a tool, hereinafter referred to generically as a bit, is frequently adjusted, or removed for sharpening, the threads in the bore of the bit block leading to the bit-receiving recess become'so worn that they no longer adequately engage the threads on the set-screw which looks the bit in its recess. The set-screw is thus worked out from its position in the bore of the bit block, releasing the bit, and becoming itself lost.

In cutter chains for use in coal mining the wear-in the threaded bore of the bit block is marked, since the set-screw must frequently be loosened to permit the removal of the bit for sharpening and adjustment. In such cutter chains, if the bit be released by loss of the setscrew, the bit tends to be forced progressively out of its recess, and may be either broken or deformed I by such excessive projection, or may become lodged in the kerf in which the cutter chain, comprising the bit and bit block, is working.

The object of my invention is to provide a set screw which will firmly engage in the threaded bore of a, bit block in spite of imperfection in the threading of the bit block, due to a. wearing away of the metal of the bit block by often repeated movement of the set-screw therein.

In the accompanying drawing, Fig. I is a side elevation showing several associated links of a coal-cutting chain, and showing particularly a bit-carrying link of the chain, with a bit locked in the bit boss, or block, of the chain by means of my improved set-screw.

Fig. II is a fragmentary detail, taken in horizontal section on line II-II of Fig. I, showing the preferred form of my set screw as inserted into the bore of a bit block to clamp a bit in position therein.

Fig. III is a cross-sectional view, taken on the line IIL-III of Fig. II, and showing the set-screw on an enlarged scale.

Fig. IV is a central, longitudinal section through one modified form of my set screw.

Fig. V is a longitudinal, sectional view through 5 another modified form of my set-screw.

Fig. VI is a plan view of the preferred form of my set-screw, illustrating a useful effect in the contour of the set-screw obtainable by heat treatment of the set-screw.

Referring to Fig. I of the drawing, reference numeral 6 designates the bitcarrying link of a cutter chain, with which are shown associated connecting links 2. The bit-carrying link has thereon a bit boss 3, having therein a diametri cally extending recess t for receiving a cutter bit. The bit 5 is shown as positioned in the recess by means of my improved set-screw, designated generally by reference numeral 6, shown as engaged in a transverse threaded bore l which leads from the forward end of bit block 3 inwardly to the bit-receiving recess l in the bit look. It will be observed that the bit 5 is supported on all sides by the embracing walls of the recess 4, and that it is clamped against lengitudinal movement in its recess by the set-screw 65.

Referring now more particularly to Figs. II and III of the drawing, it will be observed that my set-screw 6 is provided with 'a diametrically extending slot 1. This slot 7 is not of uniform 3 depth throughout, but in the median region of the set-screw is of a depth greater than the radius of the set-screw, and decreases to vanishing points at the squared, wrench-receiving region 8 of the setscrew, and at the inward bitcontacting tip 9 of the set-screw. In order to obtain the maximum effect from the set-screw, it is highly desirable that in some region, preferably the longitudinal, median region of the setscrew, the slot extend to a depth greater than 40 the radius of the set-screw. In order that the full efiect of the slotted set-screw may be obtained, it is also desirable that the threaded bore in which the set-screw is inserted have a diameter a few thousandths of an inch less than the diameter of the set-screw.

Fig. III illustrates the condition of the setscrew, as inserted into a slightly undersize bore in a bit block. In this figure of the drawing, it will be observed that the lips of the slot 1, at the peripheral surface of the set-screw, are brought together by forcing the set-screw into the undersize bore, giving a somewhat wedgeshaped appearance of the slot 1 as the structure is viewed in cross section.

As so mounted, set-screw 6 forms in effect a re sillent element placed under compression by the difference between its diameter and the diameter of the bore in which it is inserted. As, therefore, the threads of the bore I wear, by repeated loosening and tightening rotation of the set=screw in the bore, the set-screw tends to expand in compensation for such wear, continuing firmly to engage its threads with the threads of the bore 1 in spite of the progressively decreasing height of the latter threads. The set screw is thus so engaged that, in long continued use of the bit block, it does not tend to work loose and become displaced from position.

Referring to Fig. IV of the drawing, there is therein shown a set screw 10, in which the slot H is of its full depth at the bit-contacting tip -9 of the set-screw. This full depth of the slot ll decreases very gradually up to a transverse line well beyond the longitudinal, median line of the set-screw, and thence decreases in depth abruptly in its squared,wrench-receiving region 8, to a vanishing point adjacent the rearward face of the setscrew. The general effect of this modified form' of set-screw, as inserted into an undersize threaded bore, is substantially that of the preferred form of set-screw shown in Fig. II.

By so slotting the set-screw, the compression under which it is placed, and the expanding force thus created, is but in relatively slight degree greater than that obtained by the use of the preferred form. A disadvantage of the modified form of set-screw, shown in Fig. IV, is that, the face of the bit-contacting tip 9 being slotted, there is a tendency for the set-screw to bite into the bit. The advantage of this modified form of set-screw resides in the greater ease of slotting obtained by running the slot from one end face of the set screw.

Fig. V of the drawing shows a modified form of set-screw "I, in which a slot i3 extends longitudinally through the set-screw, from the face of the tip 9 through the face of the set-screw at the squared region 8. ihe slotting in this manner is the least dimcult, in any one of the three illustrated forms of set-screw, since a slotting tool may simply be run from end to end of the setscrew l2. it has the disadvantage, attendant upon slotting the face of the tip 9, of tending to bite into the bit against which the set-screw bears. It also has the disadvantage that the squared region of the set-screw, which is grasped by a wrench, is somewhat resilient, thus tending to prevent a firm engagement of the set-screw by a wrench.

It will be seen, from an inspection of Fig. IV and Fig. V, that, regardless of the longitudinal contour of the set-screw slot, it is made to extend in some longitudinal region of the set-screw to a depth greater than the set-screw radius.

Desirably, bit-block set-screws are highly hardened by heat treatment. With my improved form of set-screw, shown in Fig. II, I may obtain a valuable result by subjecting the set-screw to heat treatment after slotting. This result is the production of a bulging, or entasis, of the setscrew, intermediate its ends, and in greatest degree at the most deeply slotted region of the set-screw. By heat treating a set-screw, as shown in Fig. II, I have measured the maximum intermediate bulge in the diameter of the set-screw as approximately six thousandths of an inch, in a rearward extent, throughout the set-screw one-half inch in diameter and one and one-half inches long.

In Fig. VI of the drawing, this buiged effect, or entasis, is shown at H as produced in the set-screw 6, the entasis being greatly exaggerated for purposes of illustration. As illustrated in Fig. VI the bulged effect is produced by the tendency for the lips of the slot to spread under heat treatment. This effect is naturally, as noted, marked in the region of greatest slot depth, in which the spread between the lips of the slot is greatest, .tapering to normal diameter of the set-screw at the slot terminals.

The longitudinally intermediate bulging, or entasis, of the set-screw is of substantial value, and is of particular value when the set-screw is used to clamp in position the bit blocl; of a cutter chain. In continued use of a set-screw having this peculiarity for that purpose, the set-screw is frequently rotated through a fractional turn, to. release its pressure upon the bit. After continued use of the hardened set-screw in the softer bit block, the bulging region of the set-serew gradually scours'out in the bore of the bit hlock a'seat conforming generally to its own contour. Such scoured seat, being formed. inwardly of the bit block face, there is thus produced an engagement between the set-screw and the bore of the bit block, which tends additionally to prevent displacement of the set-screw as the threads in the bit block bore become worn.

With the intermediately bulged set-screw of Fig. VI, the diameter of the bore with respect to the normal diameter of the set-screw is of lessimportance than when the set-screw is of uniform .diameter throughout its length. Even though the diameter of the bit-block bore and the normal diameter of the set-screw be equal, the scouring effect. of the bulge will be obtained and I there will be resiiient engagement between the set-screw and the bore.

A similar effect is observable in the modified form of set-screw shown in Fig. IV. As produced by heat treatment of asst-screw having a slot formed as in Fig. IV, however, there would be a tendency to increase the diameter of the set-screw throughout all of its length, save in the rearmost portion of the squared, wrench-receiving region. For this rwson the bulging, due to heat treatment, would not produce the specific eiIect illustrated in Fig. VI. A set-screw made in accordance with the modification of Fig. IV, or the modification of Fig. V, may be caused to bulge intermediately by mechanically efi'ected distortion produced before .heat treatment.

There are incidental, but valuable, advantages in the use of my slotted set-screw= One such advantage is that the slot of the set-screw, providing space for the collection of scale, prevents scale in the bit-block bore from wedging the threads of the set-screw and bit-block bore. This is of importance in permitting the oversize diameter, either medianly of the set-screw or throughout its length. Another advantage is that. the slotted set-screw tends to contract under the turning force of a wrench when it is tightly engaged in the bit-block bore. This quality tends to facilitate intentional removal of the set-screw even though it be corroded in the bit-block bore.

As a general advantage of the invention, it may be noted that it has been necessary, in order to secure even initially firm engagement of a setscrew in the cooperating threaded bore of a bit block, that the bore and set-screw match within a very narrow tolerance. This is very difllcult to obtain, particularly if the elements be heat treated after threading. As has appeared herein, much wider tolerance is permitted by the use of the slotted set-screw.

It is clear that my improved set-screw may advantageously be used in bit blocks adapted for the mounting of various types of tool, in which the tools are frequently changed for any reason. As noted above, it is particularly advantageous in clamping the bits forming the cutting elements of cutter chains used in coal mining for cutting kerfs in coal. This is for the reason that serious results may attend the displacement of any one of a number of set-screws in the cutter chain, and because during use of the cutter chain the mounted condition of each individual cutter bit cannot continuously and accurately be observed.

While described and claimed in connection with a "bit block, such expression is to be considered matter of description and not of limitation. Utility may be found in associating the slotted setscrew with an appropriately threaded bore in other association in which the set-screw tends to work loose in the bore because of frequently repeated operation.

I claim as my invention:

1. A set-screw adapted for resilient engagement in a complementary threaded bore consisting of a threaded primarily cylindrical body having therein a longitudinal slot of varied depth extended to a maximum depth greater than a radius of the set-screw body and less than the primary dinneter of the set-screw body, the set-screw having the slot therein pre-expanded to a maximum extent at the cross-sectional plane of greatest slot depth and likewise pre-expanded to a lesser extent at cross-sectional planes of lesser slot depth with consequent bulging of the setscrew body varied with the varying depth of the slot.

2. A set-screw adapted for resilient engagement in a complementary threaded bore consisting of a threaded primarily cylindrical body having therein a longitudinal slot of varied depth exter 'ied diametrically in the median longitudinal region of the set-screw body to its maximum depth greater than a radius of the set-screw body and less than the primary diameter of the set-screw body, the set-screw having the slot therein preexpanded to a maximum extent at the cross-sectional plane of greatest slot depth and likewise pre-expanded to a lesser extent at cross-sectional planes of lesser slot depth with consequent bilging of the set-screw body varied with the varying depth of the slot.

ARTHUR L. LEE. 

